1. Field of the Invention
The present disclosure relates to a high light transmittance in-plane switching liquid crystal display device. Especially, the present disclosure relates to a high light transmittance in-plane switching liquid crystal display device in which all problems shown in the horizontal electric field type liquid crystal display device, in which the pixel electrode and the common electrode are disposed in the same level plane, and the fringe filed type liquid crystal display device, in which the pixel electrode and the common electrode are overlapped, are solved.
2. Discussion of the Related Art
The liquid crystal display device (or “LCD”) represents video data by controlling the light transmittance of the liquid crystal layer using the electric fields driven by thin film transistor (or “TFT”). According to the direction of the electric field, the LCD can be classified in the two major types; one is vertical electric field type and the other is the horizontal electric field type.
For the vertical electric field type LCD, the common electrode formed on the upper substrate and the pixel electrode formed on the lower substrate are facing with each other for forming the electric field of which direction is perpendicular to the substrate face. The twisted nematic (TN) liquid crystal layer disposed between the upper substrate and the lower substrate is driven the vertical electric field. The vertical electric field type LCD has merit of higher aperture ratio, while it has demerit of narrower view angle about 90 degree.
For the horizontal electric field type LCD, the common electrode and the pixel electrode are formed on the same substrate in parallel. The liquid crystal layer disposed between the upper substrate and the lower substrate is driven in In-Plane-Switching (IPS) mode by the electric field parallel to the substrate face. The horizontal electric field type LCD has a merit of wider view angle over 170 degrees and faster response speed than the vertical electric field type LCD.
However, for the case of the horizontal electric field type LCD in which the pixel electrode and the common electrode are disposed on the same level plane, even though the horizontal electric filed is formed between the pixel electrode and the common electrode, there is no electric field just over the pixel electrode and the common electrode. Therefore, the area occupied by the pixel electrode and the common electrode is to be the non-transmittance area at which the liquid crystal is not driven. Consequently, even the pixel electrode and the common electrode is made of a transparent material, they cannot contribute the transmittance area and then the aperture ratio will be reduced by their area.
In order to above mentioned problem, the fringe field type LCD is suggested in which the common electrode corresponding to most of all portions of the pixel area is formed at under layer, and the pixel electrode is formed upper layer by overlapping with the common electrode. In the fringe field type LCD, as the horizontal electric field is formed over the pixel electrode, the high aperture ratio can be ensured. However, the fringe field type LCD can ensure high aperture ratio at only small area LCDs. When the LCD size is larger, the parasitic capacitance formed between the common electrode and the pixel electrode is also increased. To solve this problem, the size of the transistor should be getting larger and the gap between the pixel electrodes will be narrower, so that the transmittance will be lowered.